1. Field of the Invention
This invention relates generally to a system and method for discharging a high voltage battery and, more particularly, to a system and method for discharging a high voltage vehicle battery following a vehicle damaging event or other discharging circumstance by discharging the battery to an external reference source.
2. Discussion of the Related Art
Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV), that combine a battery and a main power source, such as an internal combustion engine, fuel cell systems, etc., and electric only vehicles, such as the battery electric vehicles (BEV). These batteries can be different battery types, such as lithium-ion, nickel metal hydride, lead-acid, etc. A typical high voltage battery system for an electric vehicle may include several battery cells or modules to provide the vehicle power and energy requirements, where each battery module may include a certain number of battery cells, such as twelve cells. Different vehicle designs include different battery designs that employ various trade-offs and advantages for a particular application.
During a vehicle crash or other vehicle damaging event, the rearrangement of and/or damage to various vehicle parts and the like may cause unwanted electrical connections and the discharge of various fluids from the vehicle to occur. Because of the significant electrical power that may be stored in the vehicle battery, these things could cause potentially hazardous situations, such as electrifying of vehicle parts, chemical hazards, fire hazards, etc. Designs of vehicle battery systems need to consider these possibly harmful events.
Fault isolation detection systems are sometimes employed in electrical circuits to provide electrical fault detection. Electric vehicles are one electrical system that typically employ fault isolation detection systems to prevent a person from being harmed by high voltage on the vehicle.
In order to provide electrical fault isolation, some vehicles are equipped with a battery disconnect unit (BDU) that automatically disconnects or removes battery power from the vehicle after a crash or other event by opening battery contactors. Also, it is known in the art to employ a manual service disconnect (MSD), which is a device that separates a battery into two parts, where a trained responder responding to a vehicle crash could remove the MSD to isolate the battery. However, these known isolation techniques do not remove the charge from the battery, only contain it.
As mentioned, when a hybrid electric vehicle experiences a crash or other similar event, the integrity of the vehicle battery or other rechargeable energy storage system (RESS) always becomes a concern regardless of the degree of vehicle damage. It is desirable to discharge the battery during such an event, for example, reduce the battery voltage by half. Known battery discharge systems can be expensive, for example, thousands of dollars, and are typically heavy and require significant space. One known battery discharge system is a stand alone, embedded advanced monitoring system with DC/DC buck/boost converters including liquid cooled load banks and semi-advanced control systems. Also, compatibility between the various forms of energy storage devices in the market makes battery discharge a complicated task because of the various voltages, chemistries and current levels.